Generally, IEEE (institute of electrical and electronics engineers) is the U.S. oriented international standardization organization and has established 802.16 family s-called ‘worldwide interoperability for microwave access (WiMAX)’. The 802.16 work group established the standard for point-to-point microwave transmission, introduced OFDM (orthogonal frequency division multiplexing) for reliable transmission in NLOS (non out-of-sight) configuration, and then established the IEEE 802.16-2006, which is so-called ‘air interface for fixed broadband wireless access system’ standard, in 2004. Moreover, the 802.16 work group has established IEEE 802.16-2005 (hereinafter abbreviated ‘16e’ as the so-called ‘mobile broadband wireless access system’ standard having mobility added thereto. The so-called ‘wibro system’ is compatible with the 16e system. The Wibro system has a bandwidth of 8.75 MHz, while the 16e supports bandwidths of 3 MHz, 5 MHz, 7 MHz, 8.75 MHz and 10 MHz. Besides, IEEE is ongoing to standardize IEEE 802.16m (hereinafter abbreviated ‘16m’) that is the so-called ‘Advanced Air Interface with data rates of 100 Mbit/s mobile & 1 Gbit/s fixed’ standard. And, the IEEE 802.16m (hereinafter abbreviated ‘16m’ pertains to the so-called 4th generation mobile communication technology.
The 16m supports TDD (time division duplex) mode and FDD (frequency division duplex) mode and also supports H-FDDMS (half-FDD mobile station) mode. Unless there is a special description, frame structure characteristics and baseband processing are applied in common to all duplex modes. The 16m uses OFDMA as multiple access scheme in downlink and uplink. The frame can be called a radio frame in the following description. The frame is conceptionally discriminated from a subframe or a super frame.
OFDM symbol is generated by inverse Fourier transform. A duration time of the OFDM symbol can be called ‘useful symbol time’ Tb. A copy portion of a last Tg part of the useful symbol time is called a cyclic prefix (CP). This is used to collect plural paths and is also used to sustain inter-tone orthogonality. And, Ts is a time resulting from adding Tb and Tg together. FIG. 1 shows such a structure.
FIG. 2 is a diagram for an example of TDD frame structure of a wireless communication system having a transmission band of 8.75 MHz and ‘CP=1/8 Tb’ A system supporting this frame structure is called ‘legacy system’ For examples of the legacy system, there are the 16e system using a bandwidth of 8.75 MHz and the Wibro system. A frame used by the legacy system has a frame length of 5 ms and 43 OFDM symbols are included per frame. Since resource allocation is performed by symbol unit in the legacy system, it is possible to discriminate uplink and downlink from each other by symbol unit. In FIG. 2, 27 symbols on the left side are used for downlink, while 15 symbols on the right side are used for uplink. A ratio of downlink to uplink in the legacy system can be set to 27:15, as shown in FIG. 2. Yet, the number of uplink OFDM symbols is variable up to 12 to 18. In addition, one OFDM symbol is utilized as TTG (transmit transition gap) or RTG (receive transition gap).
Since the 16m has to support backward compatibility, it should be able to support the legacy frame structure shown in FIG. 2.